This invention relates to industrial robots, and more particularly to improvements in a horizontal articulation type industrial robot in which a first arm is rotatably mounted on the shaft of a stationary stand and a second arm is rotatably mounted at the end of the first arm.
Conventional horizontal articulation type industrial robots are shown in FIGS. 1 and 2.
As shown in FIG. 1, a first arm 12 is rotatably mounted on a stationary stand 10, and a second arm 14 extends from the end of the first arm 12. A motor 16 for driving the first arm is provided above the stationary stand 10, and a motor 18 for driving the second arm is provided on the end of the first arm 12. The end of the second arm 14 is coupled to a suitable hand 20. In this industrial robot, the first arm 12, the second arm 14 and the second arm driving motor 18 protrude sidewardly, and this part of the robot is relatively large in weight. Therefore, the arms 12 and 14 and the stationary stand 10 are liable to bend, and the robot itself is not suitable for high speed operations.
The industrial robot shown in FIG. 2 is an improvement of the robot of FIG. 1. In FIG. 2, those components which have been described with reference to FIG. 1 are designated by the same reference numerals, and a description thereof is therefore omitted.
In this industrial robot, the first arm driving motor protrudes in a direction opposite the direction of protrusion of the first arm 12, and the second arm driving motor 18 is provided with a planet type speed reducing unit 22 and is secured to the upper surface of the first arm 12 above the stationary stand 10. The output of the speed reducing unit 22 is transmitted through a shaft 24 to a bevel gear 26 at the end of the shaft 24, to rotate the bevel gear. The rotation of the gear 26 is transmitted through a bevel gear 28 to a shaft 30 integral with the second arm 14, to turn the shaft 30 and accordingly the second arm 14.
The planet type speed reducing unit 22 may be one bearing the trademark "Harmonic Drive" of Harmonic Drive Systems Co. The unit can transmit power from the input side to the output side at a predetermined gear reduction ratio. However, since the power transmitting mechanism employs gears, not only it is necessary to employ a gear adjusting means, but also it is necessary to use sealing materials for lubrication. Furthermore, the mechanism suffers from problems in that the gears are noisy and are subject to wear. In addition, the robot is disadvantageous in that the second arm 14 is liable to play owing to the backlash encountered in the use of a gear, and accordingly the accuracy of positioning operations is lowered, with the result that the robot cannot be used for assembly operations of high accuracy.
In addition to the foregoing prior art, Japanese publication No. 55-112789 discloses an industrial robot, wherein rotary drive mechanisms for the first and second arms are provided on respective rotary shafts. That is, the drive motor for the second arm is disposed on the first arm, so that the moment of inertia of the first arm is large, which is disadvantageous in the movement of the first arm. Japanese publication No. 56-62778 discloses a drive motor (17) for the second arm (12). The drive motor is disposed at a position opposite the first arm (11) with respect to a main sleeve (4). Further, bevel gearing is used for power transmission to the second arm. However, speed reduction means is disposed between the gearing and the motor, and backlash of the gearing may affect working accuracy. Even though a desirable moving balance may be obtainable in the device according to this publication, the moment of inertia is large, so that high responsiveness is not obtainable.